Optical element including a plurality of regions

ABSTRACT

An optical element comprising a body having a surface, wherein the surface has a plurality of regions periodically arranged in a tessellation, and wherein each region of the plurality of regions has a random spatial distribution of microstructures is disclosed. An optical system comprises a light source; and the optical element is also disclosed. Methods of making and using the optical element and the optical system are also disclosed.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/751,337, filed Oct. 26, 2018, the entire disclosure of which ishereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an optical element comprising a bodyhaving a surface, wherein the surface has a plurality of regionsperiodically arranged in a tessellation, and wherein each region of theplurality of regions has a random spatial distribution ofmicrostructures. An optical system comprises a light source; and theoptical element. Methods of making and using the optical element and theoptical system are also disclosed.

BACKGROUND OF THE INVENTION

In applications related to 3D scanning and gesture recognition, oneutilizes optical components to project a light pattern over a scenebeing probed, typically in association with lasers with a wavelength inthe range of about 700 nm to about 1000 nm. The light pattern depends onthe probing technique and can take various forms, such as a periodicgrid of spots, lines, stripes, checkerboards, etc.

Current techniques used to project a light pattern rely on one ormultiple diffractive optical elements to produce a certain distributionof diffraction orders. Diffractive optical elements (DOE's) arenaturally suited to the task of producing light patterns, such asdiffraction patterns. A DOE can be described as a thin surfacestructure, typically one wavelength of light, that can produce a lightpattern by interference and/or diffraction. Accordingly, a cone of lightthat is output from a DOE is defined by its minimum feature which isrelated in an inverse proportion. That is, increasingly large spreadangles require decreasingly smaller features. DOE's, however, areextremely sensitive to deviations from the design wavelength orfabrication errors with the main consequence being that the zerodiffraction order becomes much stronger than the other diffractionorders, which poses an eye-safety problem that cannot be tolerated in 3Dsensing applications.

U.S. Pat. No. 8,630,039, for example, describes DOE's to produce a spotpattern. A random spot pattern often needs to cover a wide angular rangeto be able to capture a large portion of the scene. To illuminate awide-angle scene a DOE requires a pattern with very small features. Forexample, to cover a 60-degree range with a laser of wavelength 850 nm, aDOE with 1.7 μm minimum feature would be necessary. A wider angularrange would require even smaller features. For maximum efficiency, a DOEneeds to be designed and fabricated as a grayscale, continuous phaseprofile. However, it can be challenging to produce a grayscale DOE withsuch small features. Instead, grayscale DOEs are generally produced witha binary phase profile having an efficiency of at most 80%. Theremaining energy is lost to higher diffraction orders outside of themain light pattern. The use of multiple DOEs, such as disclosed in U.S.Pat. No. 8,630,039, helps to address the zero diffraction order.However, the use of multiple DOEs has a compounding effect and practicalefficiency is around 50%-60%

SUMMARY OF THE INVENTION

In an aspect, there is disclosed an optical element comprising, a bodyhaving a surface, wherein the surface has a plurality of regionsperiodically arranged in a tessellation, and wherein each region of theplurality of regions has a random spatial distribution ofmicrostructures.

In another aspect, there is also disclosed an optical system,comprising, a light source; and an optical element including a bodyhaving a surface, wherein the surface has a plurality of regionsperiodically arranged in tessellation, and wherein each region of theplurality of regions has a random spatial distribution ofmicrostructures.

In another aspect, there is further disclosed a method of using anoptical system, including projecting an input beam from a light sourceto an optical element, wherein the optical element includes a bodyhaving a surface, wherein the surface has a plurality of regionsperiodically arranged in a tessellation, and wherein each region of theplurality of regions has a random spatial distribution ofmicrostructures; and shaping the input beam into a target pattern.

Additional features and advantages of various embodiments will be setforth, in part, in the description that follows, and will, in part, beapparent from the description, or may be learned by the practice ofvarious embodiments. The objectives and other advantages of variousembodiments will be realized and attained by means of the elements andcombinations particularly pointed out in the description herein.

DETAILED DESCRIPTION OF THE DRAWINGS

The present disclosure in its several aspects and embodiments can bemore fully understood from the detailed description and the accompanyingdrawings, wherein:

FIG. 1 is a diagram of an optical element according to an aspect of theinvention;

FIG. 2A is a representation of a plurality of regions periodicallyarranged in a tessellation according to an aspect of the invention;

FIG. 2B illustrates four regions of microstructures with a square outergeometric boundary in a tessellation, where the regions are periodicallyarranged in a repeating sequence in two orthogonal dimensions;

FIG. 2C is a representation of two regions of microstructures with asquare outer geometric boundary in a checkerboard grid;

FIG. 3 is a representation of a plurality of regions periodicallyarranged in a tessellation according to another aspect of the invention;

FIG. 4 is a representation of a plurality of regions periodicallyarranged in a tessellation according to another aspect of the invention;

FIG. 5 is a representation of a plurality of regions periodicallyarranged in a tessellation according to another aspect of the invention;

FIG. 6 is a representation of a plurality of regions periodicallyarranged in a tessellation according to another aspect of the invention;

FIG. 7 a diagram of an optical system including an optical elementaccording to an aspect of the invention;

FIG. 8 is a representation of contour plots with various microstructureswith square, circular, hexagonal, and pentagonal outer geometricboundaries;

FIG. 9 is a representation of contour plots with various microstructuresdefined by a saddle-shaped profile and combinations thereof;

FIG. 10 illustrates a target pattern with speckle produced with anoptical element according to an aspect of the present invention;

FIG. 11 is a diagram of optical elements 10 in a series in which themicrostructures are characterized by a focal length and the separationbetween the optical elements matches the focal length; and

FIG. 12 is a diagram of an optical element in which the microstructuresare characterized by a focal length and a thickness of the body betweenthe tessellation surface matches said focal length.

Throughout this specification and figures like reference numbersidentify like elements.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are intended to provide an explanation of various embodiments of thepresent teachings.

Accordingly, it is an object of the present invention to provide animproved an optical element can comprise a body having a surface,wherein the surface has a plurality of regions periodically arranged ina tessellation, and wherein each region of the plurality of regions hasa random spatial distribution of microstructures. An optical system cancomprise a light source 2, and the optical element 10.

The optical element can receive an input beam 5 from a light source 2,such as a laser. The optical element can project the input beam 5 as atarget pattern 7, 9, such as a random distribution of spots. The opticalelement can exhibit several properties, such as projecting the inputbeam 5 with high efficiency, and/or projecting the target pattern 7, 9with speckle without a higher intensity in the zero diffraction order.In an aspect, the optical element can project the input beam 5 as atarget pattern 7, 9 with speckle that does not change with any movementof the light source 2 with respect to the optical element.

FIG. 1 illustrates an optical element 10, according to an aspect of theinvention, including a body 11 having a surface 12, such as a firstsurface 12a and a second surface 12 b. FIG. 7 illustrates an opticalsystem 100 including a first optical element 10 a in series with asecond optical element 10 b, according to another aspect of theinvention. Each of the first optical element 10 a and the second opticalelement 10 b can be similarly described. For example, first opticalelement 10 a can include a first body 11 a having a surface 12, such asa first surface 12 a and a second surface 12 b; and a second opticalelement 10 b can include a second body 11 b having a surface 12, such asa first surface 12 a and a second surface 12 b. For simplicity sake, thedisclosures herein relating to the optical element (10, 10 a, and 10 b),body (11, 11 a, and 11 b) and surface (12, 12 a, and 12 b) are equallyapplicable to each respective component, unless otherwise indicated.

The body 11 of the optical element 10 can include an optical material.Non-limiting examples of optical material suitable for use as the body11 include glass or plastic, such as UV-cure polymers, polycarbonate,acrylic, fused silica, silicon or varieties thereof, such as amorphoussilicon. Other optical materials can also be used. Further, the body 11can comprise a single optical material or a multiplicity of opticalmaterials bonded together in multiple layers, which can includesubstrates for mechanical support and other layers such as those foranti-reflection coating or other layers for other purposes, such as ITOand metal coatings.

The body 11 of the optical element 10 can include a surface 12, such asa first surface 12 a and a second surface 12 b. The first surface 12 acan be oppositely oriented the second surface 12 b. In an aspect, theoptical element 10 can include any number of surfaces 12, for example,one surface, two surfaces, three surfaces, etc. The number of surfaces12 of the optical element 10 can be dependent upon the shape of theoptical element 10.

The surface 12, such as the first surface 12 a and/or second surface 12b, of the body 11 can have a plurality of regions 22 periodicallyarranged in a tessellation. Each region 20 of the plurality of regions22 can have an outer geometric boundary than can abut (without gaps) anouter boundary of an adjacent region of the plurality of regions 22. Asshown in FIG. 2A, the plurality of regions 22 is periodically arranged,for example in a 3×3 array. Each region 20, such as indicated by A, B,C, and D, can be arranged in a repeating sequence in two orthogonaldimensions of the plurality of regions 22, as shown in FIG. 2B. FIG. 2Cillustrates two regions, indicated by different patterns, arranged in acheckerboard.

The outer geometric boundary of each region 22 of the plurality ofregions 20 can be any polygon shape, for example, a triangle, a square,a rectangle, a pentagon, a hexagon, a heptagon, an octagon, etc. In anaspect, each region of the plurality of regions can have a same outergeometric boundary. As shown in FIG. 2A, each region 20 can have asquare shape and the plurality of regions 22 can also form a periodicarrangement in a tessellation, also in the shape of a square. In anaspect, the outer geometric boundary can be an arbitrary shape. Eachregion 20 can include a random spatial distribution of microstructures,such as saddle-shaped microstructures. As shown in FIG. 3, each region20 can have a hexagon shape and the plurality of regions 22 can form aperiodic arrangement in a tessellation, in an arbitrary shape. In anexample, each region 20 can include a random spatial distribution ofsaddle-shaped microstructures.

In an aspect, two or more regions 20 of the plurality of regions 22 canhave different outer geometric boundary in a tessellation. As shown inFIG. 4, a first region 20 a, of the plurality of regions 22, has anouter geometric boundary in a hexagon shape. A second region 20 b, ofthe plurality of regions 22, has an outer geometric boundary in anelongated diamond shape. The plurality of regions 22 includes a firstregion 20 a and a second region 20 b, in which the outer geometricboundary of the first region and the second region are different. FIG. 5illustrates a plurality of regions 22 in which a first region 20 a hasan outer geometric boundary in a pentagon shape. A second region 20 b,of the plurality of regions 22, has an outer geometric boundary in ahexagon shape.

The tessellations can be simple, as shown in FIGS. 2-3, for example,including each region 20 of the plurality of regions 22 having a sameouter geometric boundary. In an aspect, the tessellations can becomplex, as shown in FIGS. 4-6, for example, two or more regions 20 (20a, 20 b, 20 c, 20 d) of the plurality of regions 22 can have differentouter geometric boundaries. As shown in FIG. 6, the plurality of regions22 includes a first region 20 a having an outer geometric boundary in apentagon shape, a second region 20 b having an outer geometric boundaryin a hexagon shape, a third region 20 c having an outer geometricboundary in an elongated diamond shape, and a fourth region 20 d havingan outer geometric boundary in an arbitrary shape, such as a star shape.

Any number of regions 20 can be used in the plurality of regions 22.Additionally, or alternatively, each region 20 of the plurality ofregions 22 can have a same or different random spatial distribution ofmicrostructures. The regions 20 of the plurality of regions 22 can beplaced in a periodic arrangement to form a tessellation for bestcontrast in the target pattern 7, 9.

Each region 20 can have a different random spatial distribution from oneanother. To be clear, each region 20 can be formed by the random spatialdistribution of microstructures within the region 20. The randomdistribution of microstructures can be based upon the size of theregion, the size of the microstructures, other variables, andcombinations thereof. The random spatial distribution of microstructureswithin each region 20 can minimize periodic artifacts in a targetpattern 7, 9 and can create a random spot distribution in a targetpattern 7, 9.

Referring to FIG. 1 again, the optical element 10 can include a body 11with a first surface 12 a having a plurality of regions 22 periodicallyarranged in a tessellation, such as a first tessellation. The body 11can include a second surface 12 b having a plurality of regions 22periodically arranged in a tessellation, such as a second tessellation,that is either the same or different from the first tessellation of thefirst surface 12 a.

Referring again to FIG. 7, there is disclosed an optical system 100. Theoptical system 100 can include a light source 2; and an optical element10 a, 10 b. The optical element 10 a can include a first body 11 a, andoptical element 10 b can include a second body 11 b, as shown in FIG. 7.Each of the first body 11 a and the second body 11 b can be as describedabove with regard to the optical element 10 in FIG. 1. For example,first body 11 a can have a surface 12 a having a plurality of regions 22periodically arranged in a tessellation, such as a first tessellation,and in which each region 20 of the plurality of regions 22 has a randomspatial distribution of microstructures. As another example, second body11 b can have a surface 12 b having a plurality of regions periodicallyarranged in a tessellation, such as a second tessellation, and in whicheach region 20 of the plurality of regions 22 has a random spatialdistribution of microstructures. In this manner, first body 11 a canreceive an input beam 5 from the light source 2 and can output a targetpattern 7 based upon the first tessellation. Second body 11 b canreceive the target pattern 7 and can output a second target pattern 9based upon the second tessellation.

In the case of two surfaces 12 a, 12 b on a single body 11 (FIG. 1) orwith a first surface 12 a on a first body 11 a and a second surface 12 bon a second body 11 b (FIG. 7), it can be possible to extend the angularrange of the target pattern 7, 9. In this case, one of the surfaces 12a, 12 b can take the form of a microlens array.

Referring again to FIG. 2A, the dashed square shows a region 20 of theplurality of regions 22 in which each region 20 has a random spatialdistribution of microstructures. In an aspect, each region 20 of theplurality of regions 22 has an identical random spatial distribution ofmicrostructures. In another aspect, two or more regions of the pluralityof regions 22 have different random spatial distributions ofmicrostructures. The random spatial distribution of microstructures canshape an input beam 5 from a light source 2, such as a coherent lightsource, into a target pattern 7, 9, as shown in FIG. 7. Themicrostructures can be formed by a variety of methods, such asmicro-replication, hot embossing, injection-molding, reactive-ionetching, or ion-beam milling, or single-point laser writing, asdescribed, for example, in U.S. Pat. No. 6,410,213.

The microstructure can be defined, either in analytical or numericalform. For example, a microstructure can take the shape of a lens with aradius of curvature, conic constant, and possibly aspheric coefficients.In the publication “Efficient Structured Light Generator,” A. Betzold,G. M. Morris, and T. R. M. Sales, in Frontiers in Optics 2016, OSATechnical Digest (Optical Society of America, 2016), paper FTu5A.4,there is disclosed a microlens based on a conic profile, that is,substantially described by a radius of curvature and conic constant.However, it has been found that the use of saddle lenses ormicrostructures, as described in U.S. Pat. No. 7,813,054 to Sales, whichis incorporated herein by reference, by themselves or in combinationwith conic lenses provides further improvements due to its ability togenerate uniform spot patterns. The microstructures of each region 20can include a saddle shape. Other microstructures can be used in eachregion 20 other than those which are saddle shaped.

The saddle shaped microstructure can have a sag function defined asfollows:

$\begin{matrix}{{{s\left( {x,{y;p}} \right)} = {\alpha \sqrt[p]{R_{x} - \sqrt[p]{R_{x}^{p} - {\left( {\kappa_{x} + 1} \right){x}^{p}}}}\sqrt[p]{R_{y} - \sqrt[p]{R_{y}^{p} - {\left( {\kappa_{y} + 1} \right){y}^{p}}}}}},} & (1)\end{matrix}$

where a is a real constant, R_(x) and R_(y) denote radii of curvature,and κ_(x) and κ_(y) are conic constants, and p is a real number, in thesimplest case. The microstructures can also be defined as follows:s(x,y)=axy, (2) where again a is a real constant. Because of theirvisual appearance, the microstructures described by Eqs. (1) and (2) aresaddle shaped lenses.

FIG. 8 illustrates contour plots of a microstructures, in which theouter geometric boundary is circular, square, hexagonal, and pentagonal.The outer geometric boundary can be defined mathematically by a functionand general boundary functions, including irregular boundaries, polygonboundaries, and arbitrary shape boundaries. Contour diagrams ofsaddle-shaped microstructures, as described by Eqs. (1) and (2), andcombinations thereof with a square boundary are shown in FIG. 9. Otherrelevant properties of saddle shaped microstructures are described inU.S. Pat. No. 7,813,054, the disclosure of which is hereby incorporatedby reference.

As discussed above, the optical system 100 can generate a target pattern7, 9 with a random distribution of spots. The optical system 100 canalso include other components, such as sensors and computer algorithmsfor scene scanning and depth profiling.

The target pattern 7, 9 can be a random distribution of spots inaccordance with the random spatial distribution of microstructures ineach of region 20 of the plurality of regions. The random spatialdistribution of microstructures can shape an input beam 5 from a lightsource 2 into a target pattern 7, 9 with speckle. The randomdistribution of spots can be over a specified angular range, and thesame or different in two perpendicular directions. Such randomdistribution of spots, without a zero diffraction order higher intensityand fixed speckle with respect to an illumination motion can be usefulin providing structured light in applications for 3D sensing.

In an aspect, a period, defining the periodic arrangement of each regionhaving 20 in the tessellation, can be smaller than a size of the inputbeam 5 in order to increase the contrast of the target pattern 7, 9 andfix any speckle in the target pattern 7, 9 from varying with anymovement of the input beam 5 relative to the optical element 10.

A target pattern 7, 9 can be created whereby a zero diffraction order isindistinguishable from others of interest in the random distribution ofspots in terms of intensity. The zero diffraction order intensity canprovide the same energy content as any other spot in the randomdistribution of spots. In this way, any issues related to eye safety canbe eliminated. In addition, typically a single surface pattern can beused to produce a target pattern 7, 9, which ensures high efficiency.Multiple optical elements 10 a, 10 b used in series, such as illustratedin the optical system of FIG. 7, can be utilized for other reasons, suchas to increase the effective input beam 5 range beyond what can bemanufactured by existing fabrication methods. In such condition, one theoptical elements 10 a, 10 b can be a simple microlens array.

Each region 20 of the plurality of regions 22 can determine the angularseparation between two spots by a grating equation (for normalincidence):

$\begin{matrix}{{{\sin \; \theta_{m}} = {m\; \frac{\lambda}{\Lambda}}},} & (3)\end{matrix}$

where θ_(m) is a diffraction angle for order m, λ is the wavelength ofthe input beam, and A is a grating period. The overall tessellationgeometry can have a direct correlation to the random spatialdistribution of the microstructures. For instance, a square arraytessellation (see e.g. FIGS. 2A-2C) produces diffraction orders on asquare grid. Similarly, a hexagonal grid tessellation (see e.g., FIG. 3)produces orders on a hexagonal grid. The angular spacing depends on thegrating period, which can be the same or different along differentdirections. The random spatial distribution of microstructures canproduce a complex random spot distribution depending upon the periodicarrangement of each region 20 in the plurality of regions 22 to producea tessellation. The tessellation geometry can determine the spotgeometry, whereas each region 20 of the plurality of regions 22determines the distribution of power among the various diffractionorders. In other words, the microstructures within each of the regions20 have diffraction orders which by being either “turned on or off”create the random spot pattern.

A method of making an optical element, can comprise, selecting aperiodic arrangement of a plurality of regions 22 to form atessellation. The method also includes assigning each region 20 within aplurality of regions 22 to form a grating period. The method alsoincludes randomly spatially distributing microstructures within eachregion 20 to form a plurality of regions. In an aspect, themicrostructures within each region can include saddle shapedmicrostructures alone, or with other shaped microstructures.

Microstructures, such as those described in U.S. Pat. No. 7,813,054, canproduce a random speckle pattern when used in isolation. In other words,a region 20 of microstructures when receiving an input beam 5 from alight source 2, such as a laser, can give rise to a target pattern 7, 9with speckle and low resolution. Depending on the particular location ofeach region 20 that receives the input beam 5, the speckle pattern canvary.

The periodic arrangement of a plurality of regions 22 to form atessellation can inhibit a movement of the target pattern 7, 9 withspeckle in the event of movement of the light source 2 with respect tothe microstructures. In this case, the target pattern 7, 9 can be saidto be frozen in place. Furthermore, the periodic arrangement of theplurality of regions 22 can lead to an increase in the contrast of thetarget pattern 7, 9 that makes it useful for 3D sensing applications. Apicture from a target pattern 7, 9 with speckle from an actualimplementation of the optical element 10 is shown in FIG. 10, whenilluminated by a light source 2, such as a laser of wavelength 633 nm.

The microstructures within each region 20 can have a specific focallength. In an aspect, a focal length on a first surface 12 a can match afocal length on a second surface 12 b regardless if two optical elements10 a, 10 b (FIG. 11) are used in series or a single optical element 10is used (FIG. 12). Because of the mirror symmetry, when placed againsteach other each microstructure in one optical element 10 faces itsmirror image in the other.

There is also disclosed a method of using an optical system 100,including projecting an input beam 5 from a light source 2 to an opticalelement 10, wherein the optical element 10 includes a body 11 having asurface 12, wherein the surface 12 has a plurality of regions 22periodically arranged in a tessellation, and wherein each region 20 ofthe plurality of regions 22 has a random spatial distribution ofmicrostructures; and shaping the input beam 5 into a target pattern 7,9. The method can also include fixing any speckle from the randomspatial distribution of microstructures from varying with any movementof the input beam 5 relative to the optical element 10.

This scope disclosure is to be broadly construed. It is intended thatthis disclosure disclose equivalents, means, systems and methods toachieve the devices, activities and mechanical actions disclosed herein.For each composition, diffractive optical element, optical system,method, mean, mechanical element or mechanism disclosed, it is intendedthat this disclosure also encompass in its disclosure and teachesequivalents, means, systems and methods for practicing the many aspects,mechanisms and compositions disclosed herein. Additionally, thisdisclosure regards a composition and its many aspects, features andelements. Such a composition can be dynamic in its use and operation,this disclosure is intended to encompass the equivalents, means, systemsand methods of the use of the composition and/or pigment of manufactureand its many aspects consistent with the description and spirit of theoperations and functions disclosed herein. The claims of thisapplication are likewise to be broadly construed.

The description of the inventions herein in their many embodiments ismerely exemplary in nature and, thus, variations that do not depart fromthe gist of the invention are intended to be within the scope of theinvention. Such variations are not to be regarded as a departure fromthe spirit and scope of the invention.

What is claimed is:
 1. An optical element comprising: a body having asurface, wherein the surface has a plurality of regions periodicallyarranged in a tessellation, and wherein each region of the plurality ofregions has a random spatial distribution of microstructures.
 2. Theoptical element according to claim 1, wherein each region has an outergeometric boundary.
 3. The optical element according to claim 1, whereintwo or more regions of the plurality of regions have different outergeometric boundaries.
 4. The optical element according to claim 1,wherein each region of the plurality of regions has a same outergeometric boundary.
 5. The optical element according to claim 1, whereineach region can be arranged in a repeating sequence in two orthogonaldimensions.
 6. The optical element according to claim 1, wherein eachregion of the plurality of regions has an identical random spatialdistribution of microstructures.
 7. The optical element according toclaim 1, wherein two or more regions of the plurality of regions havedifferent random spatial distributions of microstructures
 8. The opticalelement according to claim 1, wherein the microstructures are saddleshaped.
 9. The optical element according to claim 1, wherein the bodyhaving a surface includes a first surface and a second surface.
 10. Theoptical element according to claim 9, wherein the second surface isoppositely oriented the first surface.
 11. The optical element accordingto claim 1, wherein the body also has a second surface, wherein thesecond surface has a plurality of regions periodically arranged in asecond tessellation, and wherein each region of the plurality of regionshas a random spatial distribution of microstructures.
 12. An opticalsystem, comprising: a light source; and an optical element including abody having a surface, wherein the surface has a plurality of regionsperiodically arranged in a tessellation, and wherein each region of theplurality of regions has a random spatial distribution ofmicrostructures.
 13. The optical system according to claim 12, whereinthe light source is a coherent light source.
 14. The optical systemaccording to claim 13, wherein the coherent light source is a laser. 15.The optical system according to claim 13, wherein the optical elementprojects a target pattern in accordance with the random spatialdistribution of microstructures.
 16. The optical system according toclaim 15, wherein the target pattern is a random distribution of spotsover a specified angular range.
 17. The optical system according toclaim 15, wherein the target pattern is different in two perpendiculardirections.
 18. The optical system according to claim 12, wherein aperiod defining the periodic arrangement is smaller than a size of aninput beam from the light source in order to increase a contrast of atarget pattern and fix speckle.
 19. A method of using an optical system,comprising: projecting an input beam from a light source to an opticalelement, wherein the optical element includes a body having a surface,wherein the surface has a plurality of regions periodically arranged ina tessellation, and wherein each region of the plurality of regions hasa random spatial distribution of microstructures; and shaping the inputbeam into a target pattern.
 20. The method according to claim 19,further comprising fixing any speckle from the random spatialdistribution of microstructures from varying with any movement of theinput beam relative to the optical element.